Flat MRI Magnet Shimming for Homogeneous Field Access
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Solution Overview
Problem
Existing Magnetic Resonance Imaging machines with open magnet structures face challenges in achieving magnetic field homogeneity due to their complex geometric shapes, which limits access to the imaging volume and results in energy losses and inability to control the homogeneity region.
Innovation Solution
A method that corrects inhomogeneity of the magnetic field by using a flat magnet with a polynomial solution to Laplace's equation on a spherical cap, allowing for a homogeneous magnetic field within a volume bounded by a spherical cap surface, achieved through the positioning and calculation of correction elements on a ferromagnetic pole piece.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gantry structure with opposed magnetic field generating elements is used, then magnetic field homogeneity can be achieved, but access to the imaging volume is limited
Solution Approach 1:
The patent applies asymmetry by transitioning from a symmetric gantry structure with opposed pole pieces to an asymmetric single-sided magnet configuration. The magnet consists of a single flat plate element positioned on one side only, creating an asymmetric magnetic field distribution that is then corrected using shimming techniques to achieve the desired homogeneity in the imaging volume while maintaining open access from all other directions.
Solution Approach 2:
The patent applies segmentation by dividing the magnetic field correction function into separate correction elements (shimming components) that are independently positioned and adjusted. These correction elements are distributed across the imaging space to locally compensate for field inhomogeneities, allowing the system to achieve uniform field distribution without requiring a closed gantry structure.
2Ease of operation
If a flat single-plate magnet structure is used, then access to imaging volume is improved, but magnetic field homogeneity cannot be maintained
Solution Approach 1:
The patent introduces correction elements as intermediary components between the flat single-plate magnet and the imaging volume. These correction elements act as mediators that generate compensating magnetic fields to counteract the inhomogeneities produced by the simplified magnet structure, thereby enabling both open access and field homogeneity to coexist.
Solution Approach 2:
The patent applies parameter changes by systematically adjusting the position, size, and magnetic properties of correction elements to optimize field homogeneity. The shimming process involves varying multiple parameters of the correction elements until the desired field uniformity is achieved in the imaging volume, transforming the initially non-uniform field into a homogeneous one.
3Reliability
If complex geometric magnet shapes are used to create homogeneity region, then field homogeneity can be achieved, but device complexity increases and energy losses occur
Solution Approach 1:
The patent extracts the geometric complexity from the magnet structure itself and relocates it to separate correction elements. Instead of shaping the main magnet into complex geometries to achieve field homogeneity, the solution removes the simplicity of the flat plate magnet and adds distributed correction elements that carry the geometric complexity, separating the functions of field generation and field correction.
Solution Approach 2:
The patent transitions from two-dimensional geometric shaping of the magnet to a three-dimensional distribution of correction elements in space. The correction elements are positioned at various locations and orientations throughout the imaging volume, using spatial distribution in multiple dimensions to achieve field homogeneity rather than relying on complex 2D cross-sectional shapes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables easy access to the imaging volume, minimizes energy losses, and provides a homogeneous magnetic field on a spherical cap, improving the design of MRI machines for dedicated applications like breast, head, or limb imaging.
Implementation Method 1
generating a polynomial that represents the static magnetic field generated by the magnet
Implementation Method 2
calculating position and magnitude parameters of one or more correction elements to obtain the desired field characteristics
Data Source
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AI summary
The present invention relates to a method of correcting inhomogeneity of the static magnetic field generated by the magnet of a Nuclear Magnetic Resonance imaging machine, wherein the magnet is flat and the magnetic field on one side of said magnet is corrected such that a volume is defined, which is bounded by a spherical cap surface, in which volume and along which surface the magnetic field is homogeneous, i.e. has field lines having equal parallel directions and equal intensities.